| Popis: |
Compression and shear wave propagation was studied in pressed polycrystalline salt. The experimentally observed longitudinal profiles and the delta sub x-V relation obtained from these profiles were similar to the uniaxial strain data. Shear wave profiles showed very rapid attenuation with propagation. Beyond 7-8 mm depth, negligible shear particle velocities were observed. The onset of the shear signal and the observed structure in the profiles were difficult to interpret because of the experimental artifacts related to the preceding longitudinal wave. A material constitutive model for salt was constructed based primarily on static data. Pressure-volume relations are described by a porous solid description. An isotropic-elastic-viscoplastic- strain hardening model describes the deviator stress-strain relations. The constitutive model gave reasonable simulation of the static and dynamic uniaxial strain data. The same model predicted a strong attenuation of the shear particle velocities with propagation distance in agreement with experimental results. However, the shear wave arrival and structure observed in the experimental profiles were not matched. The present study, though limited in scope, suggests that static data on salt provide reasonable predictions under dynamic loading. A single experiment on westerly granite gave good results. The observed shear wave amplitude was quite large and the arrival time agreed with extrapolations from ultrasonic data. |
